The present invention relates to a system for detecting an arcing fault in a DC electrical power cable; in particular, for detecting such a fault occurring in the DC power distribution system of a telecommunications network.
Arcing from electrical power cables at points of worn or damaged insulation constitutes a significant fire hazard in most building environments. This is particularly so in telephone company central offices which may remain unoccupied for considerable lengths of time. Although the DC power supply systems in these locations include protective devices, such as fuses and circuit breakers, to ensure interruption of dangerous current flow in the event of a short circuit or overload, the level and duration of momentary current surge at the instant of arcing are usually insufficient to actuate such protection devices. The heat accompanying such arcing is, however, quite capable of initiating a destructive fire.
There is thus a definite need for means by which arcing in a faulty or damaged electrical system may be detected and an alert or disconnect signal given in time to avert serious losses. An earlier detection system described in U.S. Pat. No. 5,047,724 provided such a means which operated through recognition of a characteristic frequency domain energy distribution pattern generated by the arcing itself. By continually monitoring the power supply system for the appearance of such a pattern, that earlier detection device was able to provide early warning of a hazardous arcing condition.
The present invention provides a simpler and less expensive detection device which responds directly to over-threshold levels of increased current flow indicated within a lower frequency spectrum band during an arcing event in a DC power distribution system.